How to verify image signature before writing to ota partition?

[zhouzhendong]

I understand esp_ota_end() will verify the signature of the image in the partition in update.
However, is there a function I can call to verify an image file before writing it to partition?
My use case is: the image file is first uploaded and saved in an sdcard file system. Then I want to validate the image before writing to OTA partition (esp_ota_begin/esp_ota_write/esp_ota_end).
Thanks